The present invention relates to the location and guidance of a moving body equipped with a linear camera.
It finds one application in the location and/or guidance of a motor vehicle driving along a roadway along which fixed beacons are distributed which define a reference path, the beacons being intermittently illuminated either actively (intermittently emitting sources) or passively (retroreflective beacons illuminated by a flash).
A number of techniques for locating and guiding motor vehicles are already known.
One of these techniques, known as the xe2x80x9cwire guidancexe2x80x9d system consists in continuously slaving the motor vehicle to a conductive wire embedded in the ground and powered at a chosen frequency.
Another known technique consists in slaving the motor vehicle to magnetic markers, embedded in the ground. One or more detectors on board the vehicle detect the presence of the markers as the vehicle passes over said markers, and thus allow the vehicle to be located with respect to the markers.
Yet another known technique consists in providing wire guidance along a radiating cable laid along the roadway along which the vehicle moves. A sensor on board the vehicle determines the distance between the cable and the vehicle. Slaving keeps this distance at a constant value.
Such techniques have the disadvantage of requiring infrastructures which are generally expensive to implement both in the ground and in the vehicle. Furthermore, these techniques provide information only along that portion of the route which is in the immediate vicinity of the vehicle. As a result, this information does not allow the path along the road to be predicted, and this prevents the next said path being used to regulate the speed of the vehicle.
Another known technique uses image processing to locate a moving body with respect to visible points of reference on the roadway, such as white lines. However, this technique is not satisfactory either, because of poor marking (old white lines, roadworks, puddles, reflections from the sun) which perturb the image processing.
The present invention provides a solution to the problems discussed above.
It sets out from a method for locating a moving body equipped with a camera of the type comprising a linear array of photosensitive elements, aimed in a known direction with respect to reference axes associated with the moving body, image processing means, and means for capturing information relating to the movement of the moving body.
According to a general definition of the invention, the method involves the steps consisting in:
a) distributing in the zone in which the moving body moves, fixed beacons which are intermittently illuminated either actively and/or passively,
b) at the moving body and at a chosen rate, taking a pair of different linear images of the same image field, one of the images being one in which the beacon or beacons are illuminated, the other being one in which the beacon or beacons are not illuminated,
c) processing the pair of linear images by a point-by-point subtraction of one from the other,
d) obtaining at least one bright spot from the subtraction of the two linear images, this spot representing at least one light beacon in the environment,
e) calculating, on the basis of information relating to the movement of the moving body, the position of the bright spot on the linear array, and its derivative, a first item of information relating to the distance separating the beacon thus represented and a frame of reference associated with the moving body, and a second item of information relating to the angular position of the beacon with respect to said frame of reference associated with the moving body, thus making it possible, as a function of the first and second items of information thus calculated, to locate the moving body in relative terms with respect to said beacon.
According to a first embodiment of the invention, step e) further comprises locating the moving body in absolute terms with respect to a fixed frame of reference associated with two separate beacons which can be seen simultaneously, said absolute location consisting in calculating, at a single given instant, a relative location with respect to each beacon as described hereinabove, the heading of the moving body with respect to the two beacons, and the coordinates of a chosen point of the moving body with respect to said fixed frame of reference associated with the two beacons.
According to a second embodiment of the invention, step e) further comprises locating the moving body in absolute terms with respect to a fixed frame of reference associated with two beacons which can be seen at least in turn as the moving body moves along, said absolute location consisting in calculating, at a first given instant, a first relative location with respect to a first beacon as described hereinabove, in calculating, at a second given instant, after the first instant, in calculating [sic] a second relative location of the moving body with respect to a second beacon which follows the first beacon in the direction of travel of the moving body, as described hereinabove, in using odometry to calculate the movement of the moving body and the heading of the moving body with respect to said first and second beacons and in calculating the coordinates of a chosen point of the moving body with respect to said fixed frame of reference.
Advantageously, the number of beacons are distributed along the roadway to define a reference path, and the method further comprises a step f) which consists in determining said reference path using the relative and/or absolute location of the moving body as described hereinabove, and in guiding the moving body, keeping a certain distance between the moving body and said reference path. A method such as this allows the moving body to predict the path along the route so as, for example, to regulate the speed of the moving body.
Another subject of the present invention is a device for implementing the method according to the invention.